1. Field of the Invention
The present invention relates to a thin film magnetic head comprising a read magnetic head element of a CPP structure for reading as a signal a magnetic field strength recorded on a magnetic recording medium or the like, and further relates to a head gimbal assembly and a hard disk drive each including such a thin film magnetic head.
2. Description of the Related Art
In recent years, following the improvement in areal recording density of hard disk drives, improvement in performance of thin film magnetic heads has been required. As the thin film magnetic heads, use has been widely made of composite thin film magnetic heads each having a structure wherein a reproducing head comprising a read magnetic head element dedicated for reading and a recording head comprising an induction-type electromagnetic transducer element dedicated for writing are stacked in layers on a substrate.
The read magnetic head elements can be roughly classified into two types depending on in which direction a current (sense current) for detection of a magnetic field flows with respect to an element stacking direction of the stacked element structure.
Specifically, they are roughly classified into a CIP (Current In Plane) element in which the current flows along the stacked layer planes of the stacked element structure and a CPP (Current Perpendicular to Plane) element in which the current flows in the stacking direction (perpendicular direction) of the stacked element structure.
A CIP-GMR (Giant MagnetoResistive) element can be cited as the former element, while, a CPP-GMR element or a CPP-TMR (Tunnel MagnetoResistive) element can be cited as the latter element.
Particularly, the magnetic head having the latter CPP read magnetic head element is a head aimed at by the present invention and has a structure in which upper and lower surfaces of the element are sandwiched between a lower shield layer and an upper shield layer. Normally, the lower shield layer and the upper shield layer also function as electrodes, wherein a voltage is applied across the lower shield layer and the upper shield layer so that a sense current flows in the stacking direction (perpendicular direction) of the element.
Presently, as a structure generally used for a magnetic head, there is employed a shield shape in which upper and lower shield layers shielding a read magnetic head element each have a length in an MR height direction (an inward depth direction perpendicular to an ABS (Air Bearing Surface)) which is shorter than a width thereof. This is because magnetic domains of the shield layer are made stable by setting the shape of the shield layer laterally long, thereby preventing occurrence of noise which is otherwise caused by coupling between domain wall movement of the shield layer and a free layer due to magnetic flux from a magnetic recording medium at the time of a read (reproduction) operation.
On the other hand, in the magnetic head structure, for example, at the time of signal writing, there is generation of Joule heat from a coil layer in an induction-type electromagnetic transducer element and heat caused by eddy current loss from upper and lower magnetic layers and thus there may occur a so-called TPTP (Thermal Pole Tip Protrusion) phenomenon in which an overcoat layer covering the whole element is heat expanded due to such generated heat so that the magnetic head element protrudes toward the surface of a magnetic disk. When the shield layers each having the short length in the MR height direction are employed as described above, the area of about half the coil layer is a region where no shield material exists thereunder so that the influence of the TPTP phenomenon significantly appears. By disposing a heatsink under the coil layer, it becomes possible to release the heat to the AlTiC side to thereby suppress the TPTP phenomenon. However, it is necessary to limit the propagation of the heat to the magnetoresistive effect layer (element) as much as possible to thereby keep the signal reading capability.
Further, with respect to a yearly increasing demand for higher recording densities in magnetic heads, there is required a drastic improvement in recording and reproducing characteristics at high recording frequencies, i.e. frequency characteristics (f characteristics) in a high frequency region.
The present invention has been conceived under these circumstances and has an object to provide a thin film magnetic head that can limit the propagation of heat to a magnetoresistive effect layer as much as possible by increasing an effect of heat radiation to the substrate side and, further, that can achieve a drastic improvement in recording and reproducing characteristics at high recording frequencies, i.e. frequency characteristics (f characteristics) in a high frequency region, and to further provide a head gimbal assembly and a hard disk drive each comprising such an improved thin film magnetic head.